Reaction Order
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 24
- Joined: Fri Sep 25, 2015 3:00 am
Reaction Order
Why is the reaction order the sum, rather than the products, of the orders of each reactant?
Re: Reaction Order
It might be because of the exponents; meaning, when concentrations are multiplied, you add each part's powers to get the "sum" of the power. I think this also translates to if you have different reactants in your rate law, so the order is just the number of concentrations you have in your rate law, i.e. R=k[A]^3 is third order, and R=k[A][B]^2 is also third order (see question 15.17)
-
- Posts: 89
- Joined: Wed Sep 30, 2020 9:33 pm
-
- Posts: 108
- Joined: Fri Sep 24, 2021 6:32 am
Re: Reaction Order
This is probably because when you multiply variables with exponents attached, you add the exponents instead of multiplying them. For example, a^2 * a^3 would equal a^5, not a^6. Therefore, in a reaction where the rate = k*[x]^2*[y]^1, you add the exponents 2 + 1 to get 3. This rate is a third-order reaction, then.
-
- Posts: 100
- Joined: Fri Sep 24, 2021 5:17 am
Re: Reaction Order
Follows from exponent rules I think. We add orders together because they are exponents of the concentrations.
-
- Posts: 104
- Joined: Fri Sep 24, 2021 7:08 am
Re: Reaction Order
A good way to understand this is that when exponents are multiplied together, the product is a sum of the exponents. We add the orders together because they are the product of the concentrations, which have exponents.
-
- Posts: 55
- Joined: Wed Feb 17, 2021 12:19 am
Re: Reaction Order
Hi Rachna, the reason why the reaction order is the sum rather than the products ultimately boils down to math. Specifically, exponents. As a person who is weak in mathematics, I googled this and it is because when you multiply exponents, the final answer is the the sum of both exponents. Similarly, the "product" of the concentrations when we have the reaction order, is found by summing them all up because they include exponents. So x^6 * x^7 = x^(6+7). Hope this helps.
-
- Posts: 112
- Joined: Fri Sep 24, 2021 6:06 am
Re: Reaction Order
It kind of follows exponent laws because when you do 3^2 times 3^4 you get 3^6 which is the sum of the two exponents rather than the product of them.
-
- Posts: 105
- Joined: Fri Sep 24, 2021 6:05 am
- Been upvoted: 1 time
Re: Reaction Order
Hello! So essentially the exponents are multiplied together, and the product is the sum of these exponents. Then, we can add the orders together, or the product of the yielded concentrations which have exponents that allow us to do this.
-
- Posts: 36
- Joined: Mon Jan 09, 2023 9:09 am
Re: Reaction Order
Like other said, it's really about the rules of exponents. Since the concentrations of the reactants are multiplied, the total order would be the sum of their exponents.
Return to “Kinetics vs. Thermodynamics Controlling a Reaction”
Who is online
Users browsing this forum: No registered users and 4 guests